Method of development of electrostatic images

ABSTRACT

A method of developing an electrostatic image which comprises feeding a toner, its carrier and a material having 1) a smaller apparent density than said carrier, 2) at least the same size as said carrier, and 3) an electrically conductive surface, to a surface having an electrostatic latent image, and effecting relative motion between said surface having said latent electrostatic image and the mixture of the toner, the carrier and the material.

United States Patent Inventor Masamichi Sato Saitama, Japan Appl. No. 686,668

Filed Nov. 29, 1967 Patented Sept. 21, 1971 Assignee Fuji Photo Film (10., Ltd.

Kanagawa, Japan Priority Nov. 29, 1966 Japan 41/78190 METHOD OF DEVELOPMENT OF ELECTROSTATIC IMAGES 5 Claims, 5 Drawing Figs.

US. Cl l17/17.5, 96/1 252/62.1

Int. Cl 603g 13/08 Field of Search 96/ 1;

[56] References Cited UNITED STATES PATENTS 2,965,573 12/1960 Gundlach l17/17.5 X 3,202,093 8/1965 Childress.... 96/1 X 3,318,697 5/1967 Shrewsbury 117/1 7.5 X 3,336,906 8/1967 Michalchik 117/37 L X 3,406,062 10/1968 Michalchik 915/] Primary ExaminerGeorge F. Lesrnes Assistant ExaminerR. E. Martin Att0rneySughrue, Rothwell, Mion, Zinn & Macpeak PATENTED SEP21 l9?! 0;. n dot-Manolo. 0.0 o s o INVENTOR MASAMICHI SATO BY X 1 "m w? ATTORNEYS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for developing an electrostatic latent image and more particularly, to an improved cascade developing method.

2. Description of the Prior Art A typical method of reproducing or recording an image electrophotographically is the cascade development. The cascade development consists in applying a photoconductive insulating material layer as a light-sensitive layer to an electrically conductive backing, charging the light-sensitive layer uniformly, exposing the light-sensitive layer according to an image to be reproduced whereby discharging electrostatic charges thereof according to the intensity of light and to thus obtain an electrostatic latent image in or on the light-sensitive layer according to the image, and then converting the electrostatic latent image into a visible image by the use of a developing agent. The developing agent generally consists of colored detecting particles called toner" and a carrier for holding the toner in the frictionally charging manner, transporting and contacting with the surface of a light-sensitive layer. When such developing agent is poured on a light-sensitive layer having a latent image, the toner is attracted and adhered electrostatically to the latent image, thereby the latent image being converted into a visible image. The resulting toner image is fixed on the light-sensitive layer, e.g., by treating with a solvent, or by heating, or fixed after transferred to a transfer material in similar ways.

Although a very satisfactory result is given by the foregoing procedure when using a half-tone image or lineal image such as is drawn by lines or black letters in a white background, no uniform developing of an electrostatic image is always expected, in particular, when an original has a large area of uniform image density, due to the fact that the state of electric field is not uniform in the electrostatic image zone. Xerographic regeneration of such an area draws only the outline thereof, whilst the central area is not developed or not filled with a toner unless an adjacent electrode or developing electrode kept apart slightly is arranged in the developing zone. A continuous tone image meets the similar defect and the tone reproduction is not effected favorably unless a developing electrode is used. Use of a developing electrode, however, impedes the flow ofa developing agent markedly in a continuous automatic apparatus, thereby resulting in lowering of the processing speed of the apparatus and, sometimes, a dangerous stoppage of the developing agent.

In US. Pat. No. 2,593,732 is disclosed a method for overcoming these disadvantages in a statical flat plate xerographic apparatus wherein an xerographic plate is exposed to a screen pattern in addition to an image pattern to be recorded to thus decompose the image into a half-tone pattern. This method is available to compacted areas, but is accompanied by a disadvantage that the image density lacks. An image area expected to be black is reproduced as a substantially equal area of alternate black and white, thus being given a grey area rather than black.

SUMMARY OF THE INVENTION The important feature of the invention consists in feeding a mixture of a carrier and a toner, that is, a developing agent in the cascade development, and a material having a smaller apparent density then the carrier and having a surface electrically conductive as well as a size of at least the same to a surface having a latent electrostatic image and then effecting a relative motion of said surface having a latent electrostatic image, said mixture and the material.

In accordance with the method of our invention, a large, uniform image density area or continuous tone image can be achieved without use of a developing electrode, accordingly, without lowering the speed of an automatic apparatus or causing stoppage of a developing agent or decomposing into a screen pattern to give a half-tone pattern.

BRIEF DESCRIPTION OF THE DRAWINGS Further features of the invention will become apparent from the following description in connection with the accompanying drawings, wherein:

FIG. 1 is a diagrammatic illustration of one embodiment of the invention;

FIG. 2 is a diagrammatic illustration of the makeup of a developing agent;

FIG. 3 and FIG. 5 are diagrammatic illustrations of the developing condition of the invention; and

FIG. 4 is a cross-sectional view and perspective view of a conductive material used in the invention.

DETAILED DESCRIPTION OF THE INVENTION In one embodiment of the invention, as shown in FIG. 1, xerographic plate 10 comprises photoconductive insulating material layer 11 and conductive backing 12. Materials therefor may be chosen from all the available known materials. The xerographic plate is electrostatically charged uniformly in a dark place and exposed according to an original to be reproduced to dissipate the charge of the photoconductive layer selectively according to the intensity of light, thereby obtaining a latent electrostatic image correspondingly. Development of the latent image is accomplished by causing developing agent 14 in a vessel 13 to cascade on a developing zone and effecting a relative motion of the photoconductive layer surface and developing agent.

The developing agent comprises, as shown enlargedly in FIG. 2, carrier 21 adhered by frictional charging, toner adhered to the circumference thereof (not shown) and material 22 having a diameter, preferably larger than that of the carrier and a surface electrically conductive. This material will hereinafter be referred to as surface-conductive material", because this gives an effect as a developing electrode, as is illustrated in the following. The ratio of the number of carriers to that of the conductive material may be suitable determined.

As shown in FIG. 3, a relative motion is carried out between the photoconductive layer, the carrier and the conductive material. The carrier settles down during the relative motion and covers the surface of the photoconductive layer due to its larger apparent density and smaller size than those of the conductive material, while reversely, the conductive material is pushed up and separated from the carrier. Consequently, the carriers settled down from carrier layer 31 consisting substantially of the same, while the conductive material pushed up from conductive material layer 32 consisting substantially of the same. Carrier layer 31 plays the same role as in the art of the cascade development and conductive material 32 acts as a developing electrode. In conductive material layer 32, the materials are contacted with each other in the horizontal and vertical directions, preferably forming at least several layers in the vertical direction and forming an area sufficient to act as a developing electrode in the horizontal direction. The conductive material layer thus gives the same effect as a sheet of developing electrode. Although it is desirable that conductive material layer 32 is packed closely in the horizontal and verti cal directions throughout developing, the contact of the materials may be broken somewhat during developing, since said broken state can be regenerated by a relative motion to such an extent that the effect as a developing electrode is displayed well. The ratio of the number of carriers carrying a toner acting as a developing agent and the number of the conductive materials is so determined that, when carrier layer 31 and conductive material layer 32 are formed by a relative motion of the carriers and the conductive material, the carrier layer 31 has a toner sufficient to develop an electrostatic image and a thickness such that the surfaces of the photoconductive layer and the conductive material layer 32 are not widely spaced apart. For example, a thickness comprising several layers. Conductive material layer 32 has a thickness sufficient to be a developing electrode, for example, a thickness comprising several layers of the conductive materials. In general, these ratios are not restricted severely.

Examples of conductive material 22 are shown in FIG. 4. FIG. 4(a) shows glass ball or plastic ball 42 having hollow 43 and coated with electrically conductive layer 41, for example, by plating nonelectrolytically or coating an electrically conductive paint. The apparent density of the conductive material as a whole may be suitably determined by selecting a suitable volume of hollow 43 or a suitable volume of the glass or plastic ball. In FIG. 4(b) a surface of a resin ball 22 consisting of a resin 42' and foams 44 dispersed therein, is subjected to conductivity treatment to form an electrically conductive surface 41'. Control of the size and number of the foam gives an electrode sphere having a desired size and density. The example of FIG. 4(b) is one of the most readily and commercially obtainable.

FIG. 4(c) shows another example of the conductive material, which has an external appearance like a bell and comprises two hemispherical shells 45 and 46 bonded at 41. When using as a material therefore a metal of a low density or a metal of a high density, but a thin thickness, the weight thereof is small as a whole. Accordingly, the weight is small in spite of its large whole volume (spherical body), that is, the apparent density is small. Such sphere settles down in water due to slit 48, but in the air, the weight becomes very small since the inside is filled with the air. This advantages the condition of the invention. Although it is more desirous to join two hemispherical shells so that slit 48 may be completely eliminated, the slit formation is unavoidable in the manufacture on a large scale. It is relatively easy to join completely two hemispherical shells of plastic as in making ping-pong balls, and in fact, the thus obtained plastic balls are favorably adapted to the object of the invention as excellent conductive materials. FIG. 4(d) shows a further example of the conductive material, which comprises two hemispherical shells 49 and 50, the one being slightly smaller than the other and inserted in the other to form a metal capsule. This is a form that is suitable for the commercial production.

Selection of such sphere may extend to others beyond the examples of FIG. 4, for example, wherein an electrically conductive paint is foamed or an electrically conductive material such as metal is made porous. After all, it is only desired that the surface is electrically conductive, the apparent density is smaller than that of a carrier and the size is larger. If the sphere is smaller than or similar to a carrier in size, the pushup effect of conductive materials by a relative motion between the carrier and the material is small, thereby being retained some of the material on a photoconductive surface.

The size of the conductive material is to be at least the same as, and preferably several times larger than that of a carrier. The upper limit is not limited particularly. In principle, a developing zone may be covered with one large conductive material. FIG. is a diagrammatic illustration of a case where very large conductive materials, for example, being several ten to several hundred times larger than a carrier, are jointly used. In FIG. 5 a conductive ball 51 is shown with a size of several times of a carrier in size and another relatively small conductive material is also shown, that is, of several 10 times or smaller. Where large conductive call 51 covers a large part of developing zone by itself, as represented by 51-1, the developing efficiency is good, while where it mounts on smaller electrode spheres, as represented by 5l-2, the electrical contact between the smaller conductive ball is made good by the weight and accordingly, the developing efficiency (speed) is made higher.

When the weight of a conductive material is too small, the contact of the conductive materials with each other is weak, that is, their electrical contact becomes incomplete. When the weight is too large, on the other hand, a developing agent is strongly pressed, leading to damage of an image developed. Therefore, the weight of the conductive material is preferably limited to a suitable range. Our experiments teach that such suitable range covers weights ofone to several 10 81 times ofa carrier in a case where the conductive material is several to several 10 times of the carrier in size, and it covers weights of several times of a carrier to several times of the size of the conductive material itself. It is to be understood, however, that any conductive material having a weight outside the aforementioned range is available as far as the desired condition of the invention is satisfied thereby.

The shape of a carrier may be suitably chosen according to the art of the cascade development and that of the conductive material may be widely varied, although only a spherical shape has been employed in this specification for the sake of illustration. Of course, it is desirable, in order to separate a carrier layer and a conductive material layer effectively by a relative motion thereof, that the carrier and conductive material are at least of a nearly spherical form.

In the foregoing illustration, a mixture of a toner, a carrier and a conductive material, previously mixed, appears as a developing agent, but said previous mixing is not always necessary. A mixture of a toner and a carrier, and a conductive material, may be provided individually. For example, a mixture of a toner and a carrier is cascaded in a developing zone of a photoconductive layer as in the ordinary cascade development, on which conductive materials are then poured. Thereafter, the photoconductive layer and the mixture of a toner and a carrier are caused to move relatively for developmg.

It will be readily understood considering the principle of the method of the invention that a large angle of the surface of a photoconductive layer and the horizontal plane is a disadvantage. When a photoconductive layer is kept substantially horizontal, on the contrary, an external force must be added so as to cause a relative motion between the surface of a photoconductive layer and mixture of a toner and a carrier and between the mixture thereof and conductive material. Addition of such external force, for example, is carried out by vibrating in the horizontal or vertical direction. When the surface of a photoconductive layer is somewhat out of the horizontal position, a carrier layer and conductive material layer are separated through a relative motion due to the gravity.

In accordance with the method of the invention, as has been specifically illustrated, a large, compacted area having a high image density is uniformly developed without use of a fixed developing electrode and while keeping the simplicity and certainty of the ordinary cascade development.

The following examples are given in order to illustrate the invention without limiting the same.

EXAMPLE 1 A toner and a carrier for Xerox 914 (marketed by Fuji Xerox Co., Ltd., Japan) were used as a cascade developing agent and conductive material were prepared by heating the foam polystyrol resin beads (diameter: about 1 mm.) to thus foam partially and subjecting the foamed beads ranging from 1.5 to 4 mm. in diameter to nonelectrolytic plating to form a thin film of silver. The weight of one conductive material was about 1 mg. A xerox flat plate was subjected to positive corona discharge in the dark to charge positive and exposed to an original by the projection method. Then, the developing agent for Xerox 914 and silver-plated conductive materials were mixed in a proportion of 45 parts by weight (carrier 43 parts, toner 2 parts), poured on a fiat plate arranged horizontally and the fiat plate was laterally oscillated several times to separate the conductive material upwards. The flat plate was slanted to remove the developing agent. The conductive materials played a part equivalent to a sheet of developing electrode, leading to the result that an edge effect-free image was obtained and a large, compacted area was uniformly developed. The image was transferred to a sheet of white paper by the conventional electrostatic transfer method and EXAMPLE 2 A selenium flat plate which had been charged positive uniformly by corona discharge in the dark, as in Example I, was subjected to image exposure according to an original to form a latent electrostatic image. A mixture of a toner and a carrier for Xerox 914 was poured on the flat plate kept horizontally, on which the same conductive materials as in Example l were then poured, and the flat plate was oscillated in the horizontal direction. Then, the flat plate was slanted to remove the carrier and the conductive materials and a good image was left similarly to Example 1. When the resulting image was transferred to a sheet of white paper by the electrostatic transferring, an excellent reproduced image was obtained.

Since the mixture of a toner and a carrier is not mixed with the conductive material at the start in this example, the toner does not tend to adhere to the circumference of the conductive material. If the developing agent is poured on a sieve having a suitable mesh size after the development, only the mixture of a carrier and a toner passes through the mesh and the conductive materials remain thereon. Accordingly, toner-free conductive materials can always be used. When the toner adheres to the circumference of the conductive materials, their electrical connection of each other is broken and their role as a developing electrode is not sufficiently played. It is desirable, therefore, that the conductive materials and the toner are as near as possible in the frictionally charging system.

EXAMPLE 3 This example illustrates an application to an automatic continuous apparatus using a long electrofax paper comprising a conductively treated paper coated with a mixture of photoconductive zinc oxide powder and insulating resin. The long electrofax paper was negatively charged continuously and uniformly, subjected to image exposure continuously to form a latent electrostatic image and fed to a developing zone continuously. When the fax paper was moved over the developing zone where a metal plate earthed had been arranged, a developing agent consisting of conductive material and a mixture of a carrier and a toner was poured thereon. The metal plate was slightly out of the horizontal and vibrated with a microamplitude in the vertical direction. The developing agent poured from above was moved relatively by the vertical vibration, whereby to be separated into a layer of the mixture of a toner and a carrier and another layer of the conductive materials, and rolled down on the fax paper, followed by recovery in a receiving vessel. The recovered developing agent was classified into the mixture of a toner and a carrier and the conductive materials, and the conductive materials were reused for the development after removing the adhered carrier by a suitable method. In this case, a similar good result was obtained to those of the foregoing two examples.

Although, in the foregoing examples, a conductive material of foamed material was used, of which surface was subjected to conductivity treatment, a hollow glass ball or plastic ball may be used, the surface of which is similarly treated. A low density plastic ball such as polystyrene ball or a polyethylene ball the surface of which is conductivity treated, is available. Furthermore, an electrically conductive resin, for example, silver paste, may be foamed to be a sponge and finely divided.

EXAMPLE 4 A pipe of aluminum having an outer diameter of 2.5 mm. and a thickness of 0.3 mm. was cut into a length of 4-6 mm. to provide an electrode forming material (conductive material). A developing agent consisting of 30 parts of the material forming material, 40 parts of a carrier consisting of glass beads of 0.8 mm. in diameter coated with nitrocellulose and 2 parts ofa toner for Xerox 914 was used. As in Example 1, a zinc oxide electrofax paper was negatively charged, subjected to image exposure and developed to give an edge effect-free image.

EXAMPLE 5 Two hemispherical shells of aluminum having an outer diameter of 5 mm. and a thickness of 0.2 mm. was welded to form a sphere and used as an electrode forming material. A developing agent consisting of 30 parts of the electrode forming material, 30 parts of a carrier consisting of glass beads of about 0.8 mm. in diameter coated with nitrocellulose and 2 parts of a toner for Xerox 914 was used. As in Example 1, using a zinc oxide electrofax paper, a negative latent image was developed to give an image completely free from the edge effect.

EXAMPLE 6 Spherical pellets of polymethyl methacrylate each having a diameter of about 3 mm. were chemically plated with silver to make the surface electrically conductive and used as a conductive material. Using a developing agent consisting of 40 parts of the material, 50 parts ofa carrier for Xerox 914 and 2 parts ofa toner for Xerox 914 and an electrofax paper consisting of a mixture of zinc oxide and vinyl chloride acetate resin, a positive latent electrostatic image was developed to given an edge effect-free image.

The spherical pellets may be: made of polystyrene, polyethylene, polyvinyl chloride, polyamide and many other resins in place of polymethyl methacrylate, said pellets being plated chemically.

EXAMPLE 7 Cylindrical pellets of Phenoxy Resin PKDA-8080 (manufactured by Union Carbide Corp.) each having a diameter of 2-3 mm. and a length of 3-4 mm. were silver plated to make the surfaces electrically conductive and used as an electrode forming material. Using a developing agent consisting of 45 parts of the electrode forming material, 40 parts of a carrier consisting of glass beads of about 0.8 mm. in diameter coated with nitrocellulose and 2 parts of a toner for Xerox 914 and an electrofax paper as in Example 1, a negative latent image was developed to given an edge effect-free image. A number of cylindrical pellets of resins, in addition, chemically plated may be similarly used.

EXAMPLE 8 Glass spherical shells having an outer diameter of 1-1.5 cm. and a thickness of about 0.3-0.4 mm. were chemically plated with copper and used as a conductive material. Using a developing agent consisting of 25 parts of the conductive material, 50 parts of a carrier for Xerox 914 and 2 parts of a toner for Xerox 914, and an electrofax paper, a positive latent image was developed to give an edge effect-free image.

In place of the glass spherical shell, a plastic spherical shell of l-2 cm. in diameter and 0.5 mm. in thickness, chemically plated, may be used.

EXAMPLE 9 A foamed polystyrene was shaped into beads having a diameter of 3-5 mm., coated with aluminum foil to make the surfaces electrically conductive and used as a conductive material. The weight of one conductive material was 10-20 mg. 25 parts of the conductive materials, 50 parts of a carrier for Xerox 914 and 2 parts of a toner for Xerox 914 were mixed to prepare a developing agent. Developing with such developing agent resulted in no edge effect.

EXAMPLE The electrode spheres of Example 1 (dia: 1.5-3 mm.) and electrode spheres of Example 8 (dia: 1-1.5 cm.) were mixed and the developing was carried out in a manner as shown in FIG. 5. Use of a developing agent consisting of 10 parts of the smaller conductive material, 25 parts of the larger conductive material, 50 parts of a carrier for Xerox 914 and 2 parts of a toner for Xerox 914 gave a good result.

EXAMPLE 1 1 10 parts of the conductive materials (pellets) for Example 7, 25 parts of plastic tube pieces having an outer diameter of about 2 mm., and a length of 10-20 mm. and coated with copper plating, 50 parts of a carrier for Xerox 914 and 2 parts of a toner for Xerox 914 were mixed and used as a developing agent, and a latent electrostatic image was developed to give a good result.

EXAMPLE 12 Electrode sphere: 50 parts of glass beads having a diameter of about 1 mm. and chemically plated with silver Carrier 150 parts of beads of lead having a diameter of 0.15-0.20

mm. and coated with nitrocellulose Toner 1.5 parts of a mixture of carbon powder and polystyrene EXAMPLE 13 Electrode Sphere 25 parts of polystyrene beads having a diameter of about 1 mm. and chemically plated with silver Carrier 120 parts of copper beads having a diameter of about 0.2

mm. and coated with nitrocellulose Toner l.5 parts of a mixture of pulverized carbon powder and polystyrene.

In Examples 12 and 13 other operations and procedures, except for the electrode sphere, carrier and toner, were similar to those used in the preceding examples and good results were obtained.

What is claimed is:

l. A method of developing an electrostatic image which comprises (a) feeding a toner, a carrier therefore and a hollow spherical or hollow cylindrical, particulate material having (1) an electrically conductive surface, (2) a smaller apparent density than said carrier and (3) an average particle size of at least about 2 times that of said carrier to a surface having an electrostatic latent image, and (b) effecting relative motion between said surface having said electrostatic image and the mixture of the toner, the carrier and the material whereby (l) the weight of said particulate material is heavy enough to facilitate good electrical contact between said particulate materials and light enough to prevent said toner from being too strongly pressed against said surface having said electrostatic latent image and (2) most of the particulate material will rise to the top of said mixture while most of the carrier will settle at the bottom thereof when said mixture undergoes said relative motion with said surface having said electrostatic latent image.

2. A method of developing an electrostatic image which comprises (a) feeding a toner, a carrier therefore and a particulate material'( 1) having an electrically conductive surface, (2) having a smaller apparent density than said carrier, (3) having an average particle size of at least about 2 times that of said carrier to a surface having an electrostatic latent image, and (4) being composed of a nonconductive material covered with a conductive material, and (b) effecting relative motion between said surface having said electrostatic image and the mixture of the toner, the carrier and the material whereby (l) the weight of said particulate material is heavy enough to facilitate good electrical contact between said particulate materials and light enough to prevent said toner from being too strongly pressed against said surface having said electrostatic latent image and (2) most of the particulate material will rise to the top of said mixture while most of the carrier will settle at the bottom thereof when said mixture undergoes said relative motion with said surface having said electrostatic latent image.

3. A method of developing an electrostatic image which comprises (a) feeding a toner, a carrier therefore and a particulate material (1) having an electrically conductive surface, (2) having a smaller apparent density than said carrier, (3) having an average particle size of at least about 2 times that of said carrier to a surface having an electrostatic latent image, and (4) being aluminum in the form ofa tube, and (b) effecting relative motion between said surface having said electrostatic image and the mixture of the toner, the carrier and the material whereby (l) the weight of said particulate material is heavy enough to facilitate good electrical contact between said particulate materials and light enough to prevent said toner from being too strongly pressed against said surface having said electrostatic latent image and (2) most of the particulate material will rise to the top of said mixture while most of the carrier will settle at the bottom thereof when said mixture undergoes said relative motion with said surface having said electrostatic latent image.

4. The method in accordance with claim 2 wherein the conductive material is selected from the group consisting of silver and copper.

5. The method in accordance with claim 2 wherein the nonconductive material is hollow. 

2. A method of developing an electrostatic image which comprises (a) feeding a toner, a carrier therefore and a particulate material (1) having an electrically conductive surface, (2) having a smaller apparent density than said carrier, (3) having an average particle size of at least about 2 times that of said carrier to a surface having an electrostatic latent image, and (4) being composed of a nonconductive material covered with a conductive material, and (b) effecting relative motion between said surface having said electrostatic image and the mixture of the toner, the carrier and the material whereby (1) the weight of said particulate material is heavy enough to facilitate good electrical contact between said particulate materials and light enough to prevent said toner from being too strongly pressed against said surface having said electrostatic latent image and (2) most of the particulate material will rise to the top of said mixture while most of the carrier will settle at the bottom thereof when said mixture undergoes said relative motion with said surface having said electrostatic latent image.
 3. A method of developing an electrostatic image which comprises (a) feeding a toner, a carrier therefore and a particulate material (1) having an electrically conductive surface, (2) having a smaller apparent density than said carrier, (3) having an average particle size of at least about 2 times that of said carrier to a surface having an electrostatic latent image, and (4) being aluminum in the form of a tube, and (b) effecting relative motion between said surface having said electrostatic image and the mixture of the toner, the carrier and the material whereby (1) the weight of said particulate material is heavy enough to facilitate good electrical contact between said particulate materials and light enough to prevent said toner from being too strongly pressed against said surface having said electrostatic latent image and (2) most of the particulate material will rise to the top of said mixture while most of the carrier will settle at the bottom thereof when said mixture undergoes said relative motion with said surface having said electrostatic latent image.
 4. The method in accordance with claim 2 wherein the conductive material is selected from the group consisting of silver and copper.
 5. The method in accordance with claim 2 wherein the nonconductive material is hollow. 